1. Field of the Invention
The present invention relates generally to an image forming apparatus. More particularly, to a device for regulating a thickness of a developer layer formed on a developing roller of a developing unit.
2. Description of the Related Art
In general, an image forming apparatus using a one-component nonmagnetic developer includes a blade that is in contact with a developing roller. A developer layer remains on the developing roller and has a predetermined thickness. FIG. 1 illustrates an example of a developing unit employing the blade.
Referring to FIG. 1, a photosensitive drum 112 is installed in a housing 104 and has a predetermined shape. The surface of the photosensitive drum 112 is charged with a predetermined electric potential by a charging roller 114. The charged surface of the photosensitive drum 112 is partially exposed to light by a laser scanning unit 160 to form an electrostatic latent image. A developer is accommodated in a toner accommodating part 105 of the housing 104, and is supplied to the developing roller 110. The toner accommodating part 105 is provided with an agitator 106 for agitating the developer. A developer supplying roller 108 is in contact with the developing roller 110, and is rotated in the same counterclockwise direction as a rotational direction of the developing roller for supplying the developer to the developing roller 110. In the instant case, blade 124 is in contact with the developing roller 110 for regulating the thickness on the developer adhered to the surface of the developing roller 110.
The blade 124 is made of a metal sheet having a predetermined thickness suitable for having an elastic force. The blade 124 applies a substantially constant pressure to the developing roller 110. The contacting pressure, caused by the elastic force, is applied to the developer passing between the blade 124 and the developing roller 110. Thus, the developer is charged with a predetermined polarity by friction.
The charged developer collides with a bent part 128 of the blade 124 for a predetermined period of time for charging. The developer 128 accumulates on the bent part and overcomes the elastic force of the blade 124. Consequently, the developer 128 passes between the blade 124 and the developing roller 110 to form a developer layer having a constant thickness.
Referring to FIG. 2, the blade 124 is welded to a bracket 122 having a high rigidity by spot welding. The blade 124 is provided at both ends thereof with sealing members 130 for preventing the developer from accumulating on the bent part 128 of the blade 124 and leaking into the housing. However, if the sealing members 130 overlap with both ends of the blade 124, estimating the pressure exerted on the developing roller 110 of the blade 124 during blade design is impossible. For this reason, it is preferable that the sealing members 130 are in contact with both ends of the blade 124.
The resultant structure is possible to design, however; a gap G is produced between the sealing member 130 and the end of the blade 124 due to an assembling error which occurs during the manufacturing process. This gap G results in the formation of an unregulated developer layer 111, causing developer loss to occur, thus polluting both ends of the photosensitive drum 112 (FIG. 1) and the interior of the image forming apparatus. Furthermore, concentrations of the developer accumulate on both sides of a wasted toner reservoir (not shown) by the unregulated developer, and this causes the cleaning performance to deteriorate.
Accordingly, there is a continual need for a developer layer thickness regulating device for a developing unit that improves the sealing effect of a developer by regulating a thickness of a developer layer formed on a developing roller.